The invention relates to a method for removing tacky plug-shaped rubber residues from holes having a depth that is greater than their diameter, especially from holes in strainer plates, whereby the rubber is forced out in one direction such that it essentially maintains its plug shape. A particular difficulty lies in the fact that the holes due to their great depth provide a large adhesive wetting surface for the tacky rubber while at the same time only a small engaging surface for the pressing tool is provided. This problem is further enhanced by the fact that the rubber has a substantially reduced stiffness as compared to the outer walls, usually comprised of steel, of the holes to be cleaned. This results in a steep shearing tension drop over the depth of the hole at the contact surface rubber/outer wall of the hole. While in the direct vicinity of the pressing tool the shearing tension is still sufficient for a fast removal, at the opposite end of the hole the adhesion is increased due to the increased inner pressure of the rubber resulting from the pressing tool. In this technical context, the rubber must be considered a very tacky fluid. The increased rubber inner pressure acts, as for a fluid, on the mantle surface of the hole, perpendicular to the force generated by the tool. This is the reason for the fatal effect that when employing a pressing stamp the pressing resistance is actually increased. Depending on the diameter of the hole, the tackiness of the rubber, and the stiffness of the rubber, the critical depth of the hole may be determined which defines the upper limit for spontaneous removal of the rubber residues by pressing because from there the effect increasing the pressing resistance takes over. This critical hole depth is in general surpassed for strainer plates the cleaning of which is primarily addressed in the invention. Conventional strainer plates have hole depth between 25 and 40 mm for a diameter of the hole between 6 and 12 mm.
According to the prior art, a forcing-out of the plug-shaped rubber residues from deep holes is not possible as a fast method step. At most, the rubber plugs may be forced to very slowly flow out of the deep holes. The time for this flowing process is within the range of hours or even days for the commonly used dimensions of the holes of strainer plates, and this process is thus unsuitable for economical mass production. Common strainer plates comprise approximately 300 to 500 holes for the rubber to be pressed therethrough.
From German Offenlegungschrift 33 35 467 a device is known with which the holes may be cleaned by employing high-pressure media jets. The exit opening for the high-pressure medium in a known manner should be placed as closely as possible to the surface to be cleaned and, for this purpose, should be movable with a lance into the boring.
The method based on this device is suitable for removing rubber residues due to the viscoelastic properties of the rubber because the fluid jet energy is essentially absorbed by damping. Only brittle or fluid-soluble materials may be removed. Furthermore, the presence of a hole is presupposed in order to be able to introduce the lance. The method is thus only suitable for enlarging the free cross-section of holes, but not for generating a free cross-section.
The German Gebrauchsmuster 88 06 774 shows a similar device with a lance from which a pressure fluid jet should exit laterally. In order to overcome the problem of insolubility of contaminants to be removed, here oils, grease, and lubricants, in the used liquid, the use of detergents is taught. The use of detergents, however, is not recommended for the problem to be solved with the invention because the valuable material to be removed could not be used any longer as a raw material, but would become refuse. Also, to complicate matters further, the detergent must be cleaned from the walls of the hole in a second cleaning step. Furthermore, as pointed out above in the aforementioned prior art, a lance cannot be introduced into the hole because it is completely plugged with rubber instead of the wall of the hole being merely covered with rubber.
In the past, strainer plates have been cleaned by boring. With this method, a hole may be cleaned within approximately 10 seconds. In addition to the considerable bore tool wear the method further suffers especially from the time-consuming centering of the bore tool axis with respect to the center of the hole since the bore tool must have an outer diameter corresponding almost to the inner diameter of the hole to be cleaned in order to provide an acceptable cutting effort. When the centering is flawed, in addition to the bore tool the walls of the hole would be abrasively loaded. Due to the considerable positioning efforts it is hardly possible to clean a plurality of holes simultaneously by boring out the rubber. For a strainer plate with, for example, 400 holes the cleaning process by boring requires approximately one hour.
A further disadvantage of the boring method lies in the fact that the personnel requirements are high. The shavings removal and the cutting edge quality of the boring tool must be constantly checked, the boring tool must be removed, ground, and reinserted, and the boring tool cooling must be controlled.
It is therefore an object of the invention to provide a less sensitive method for cleaning deep holes from rubber residues, especially holes of strainer plates, which may also to a greater extent be automatized.